Steven Hassan on WGBH Greater Boston with Emily Rooney 4/23/13

The picture slowly emerging is that Tamerlan Tsarneav was an embittered 26-year-old who found meaning in radical Islam. But friends describe 19-year-old Joh-Khar Tsarneav as a popular and fun-loving classmate. So what led the younger brother to allegedly perpetrate the horrific violence of the past week? What kind of control, if any, did the older brother exert on the younger? To help answer that, Steven Hassan, a counselor who specializes in cult-like behavior. He's also the author of the book "Freedom of Mind: Helping Loved Ones Leave Controlling People, Cults and Beliefs."